Chemical pulping process



Patented Dec. 3, 1929 ED .STTES COMPANY, OF ERIE, PEIQ'NSYLVANIA,

PATENT OFFICE A CORPORATION OF PENNSYLVANIA CHEMICAL PULPING PROCESS No Drawing. Application filed February This invention relates generally to the preparation by chemical processes of pulp or fiber such as is used in the manufacture of paper.

It is well known that, in the preparation of fiber, such as wood pulp, by mechanical processes, the product is contaminated with lignin and resinous materials which turn brown on exposure to light. Because of this and also because the mechanically prepared fibers are short and do not mat well, pulp of this character is restricted for use only in the manufacture of cheap paper such as newspaper.

lhe chemical processes differ from the mechanical processes in the important particnlar that they function to dissolve the lignin and resinous and fatty materials so that they can be drawn ofl trom the product leaving the fiber or pulp in an uncontaminated condition. Pulp of this character is used in the manufacture of the better grades or" paper.

In addition to cellulose, which forms from 4.0 to 45 per cent of fibrous materials such as spruce wood and which represents the most useful portion of the material, other carbohydrates, such as heXoses, hexosans, pentoses and pentosans, are present in proportions ranging from 23 to 28 per cent, the remaining 25 to 35 per cent representing the undesirable lignin, fats, and resinous materials referred to. The other carbo-hydrates, the heXoses, hexosans, pentoses and pentosans, can be usetully employed it retained With the cellulose but they are not so resistant as cellulose to the cooking action of the digesters and some of these carbo-hydrates are broken down into soluble products along With the lignin and resinous material. The result has been thatcarbo-hydrates have been dissolved and removed from the pulp with the ligninand resinous substances. The removal of carbohydrate material is, of course, wasteful and a general object of the present invention is to provide for the removal of the undesirable lignin and resinous content of the material Without a corresponding removal of carbohydrate substances.

ln order to protect the less stable carbohydrates against the hydrolyzing effect of the cooking solutions and the resulting breaking 16; 1927. Serial No. 168,838.

down of the carbo-hydrates into soluble products, attempts have been made to obtain the desired results by employing lower temperatu'res and a longer cooking period. An increase in yield of pulp has been obtained by this method but the increase has been rela-' tively small and the total gain in efiiciency very slight when the increased cost of processing produced by the longer cooking period is taken into account.

My invention contemplates a more effective and more economical method of protecting the carbo-hydrates from being dissolved during the cooking operation than that practised in prior operations. I have found that by adding a solution of carbo-hydrates to the cooking liquor, the solid carbohydrates contained in the wood pulp are protected from the dissolving action of the liquor. By thus preventing the dissolving of the carbo-hydrates contained in the Wood, 1 have found that Without increase of the time 'period of cooking a much higher yield of fiber is obtained than is possible by present or heretofore known methods of operation.

I have also found that a convenient'and efiicient Way of supplying the soluble carbohydrates required in the cooking liquor is to add to the fresh cooking liquor an appropriate proportion or" Waste cooking liquor from a previous cooking operation and from which the soluble 'lignin compounds have been removed. The removal of the lignin compounds either completely or in part is essential to the efiectiveness of the operation because in this way a cooking liquor is provided which contains a content or excess ofsuch as has been outlined, I havehad satis- 1 cium oxidewhich reacts with the lignin to form a precipitate readily separable from the liquid. Upon the removal of the tated lignin the waste liquor is adde to the fresh cooking liquor for the carrying out fine myself to the use ofcalcium oxide for precipitation of the lignin preparatory to:

its removal from the liquor, it being apparent that'other methods for treating the liquor for precipitating employed.

The method herein described is intended merely, to illustrate and'not to limit my invention which consistsbroadlyin adding to an acid or neutral cooking liquor carbo hydrates for'the purpose of protecting the carbo-hydratescontained in the wood fiber from being dissolved during the cooking operation, it being evident. that the retention of the solid carbo-hydrates in the fiber results in an increase in the yield of pulp produced in the'cooking operation.

Illhe terms and expressions which I have employed are used as terms .of description 5' and not of limitation, and I have no intention, in the use of such terms and expressions of excluding any equivalents of the features described, or portions thereof, but recognize precipiof the operation as described. I do not conthe lignin may be fibrous material in a solution formed of substantially equal volumes of fresh liquor and waste liquor from'which lignin compounds have been removed.

5. The process of making pulp from fibrous material which comprises cooking the fibrous material in a solution formed of subf stantially equal volumes of fresh liquor and waste liquor containing carbohydrates and from which lignin compounds have been removed. a v

6.-The process. of making pulp from fibrous material which comprises treating waste liquor containing carbo-hydrates with calcium oxide to precipitate lignin compounds, in removing the precipitated matter, in adding the liquor thus treated to an equal volume of fresh cooking liquor, and

in cooking the fibrous materialin the liquor thus produced. Y

7. The process of cooking vegetable fibrous material with an acid or neutral cooking liquor, to which carbo-hydrates substantially free from lignin have been added.

BJARNE JOHNSEN.

that various modifications are possible with- 40 in the scope of the invention claimed.

-What I claim is: 1. The process of cooking vegetable fibrous material with a cookin liquor to which has been added a solution 0% waste cooking liquor containing carbo-hydrates, from which the lignin compounds have been wholly or partly removed.

2. The method of preparing a cooking liquor containing carbo-hydrates which con- 59 sists in treating waste cooking liquor with a base in sufiicient quantity to remove a large proportion of the lignin contained therein but retaining in the solution a large part of its content of carbo-hydrates, separating the solid precipitate from the waste liquor so treated, and adding the resulting waste liquor to fresh cooking liquor.

3. The process of making pulp from fibrous material which comprises cookin the so fibrous material in a solution formed of fresh .liquor and waste liquor containing dissolved carbo-hydrates and substantially free from lignin compounds.

4. The process of making pulp from fibrous material which comprises cooking the 

